Thermoformable panel for shelves

ABSTRACT

The present invention relates to a thermoformable panel for shelves composed of: at least one core plate having a honeycomb structure composed of a plurality of adjacent cells; a coating layer that includes at least one thermoplastic material coupled to the core plate on at least one face of the core plate. The invention envisions using coating films for the honeycomb core plate that improve adhesion between the material of the honeycomb core plate and the coating films, as well as optional finishing layers overlapped thereon, reducing costs in relation to present honeycomb panels by simplifying manufacturing processes, all while maintaining elevated properties of mechanical strength and low density, and therefore a low weight.

TECHNICAL FIELD

The present invention relates to a thermoformable panel for shelvescomposed of:

at least one core plate having a honeycomb structure composed of aplurality of adjacent cells;

a coating layer comprising at least one thermoplastic material iscoupled to said core plate on at least one face of said core plate.

BACKGROUND ART

Thermoformable panels with a honeycomb core coated on at least one face,preferably on the two opposite faces, with a coating layer are known.

Currently such panels are mainly made by spraying on a honeycomb coreplate made of paperboard or the like a mixture of fibers andpolyurethane. The technology is known by the name Baypreg. The panelsobtained in this manner can be three-dimensionally shaped in a mould bycompression molding.

Baypreg technology allows thermoformable panels having a low specificweight and an optimal mechanical strength to be obtained, however theyare quite expensive and moreover the operations for spraying thepolyurethane on the honeycomb cores involve dirtying problems for theoperating members of the product lines.

Currently attempts have been made for obtaining thermoformable panels ofthe type described above by laminating sheets or films of thermoplasticmaterials on the faces of the honeycomb core. However such attempts havenot lead to considerable results, since, when bending (particularly inhot tests) the coating layers made by lamination or by another type ofconnection of sheets or films to the core layer are subjected totensile, compressive and shearing stresses that cause them to bedetached from the core plate consequently losing the chemical physicalbonds and causing the mechanical properties to cease.

Since this type of panels have a possible use in a great amount ofdifferent fields, from automotive to furnishings and furniture, as wellas structural elements in the building field, it is of great importancethe possibility of obtaining panels of this type, more easy to befabricated and more cheap, moreover without facing a reduction in themechanical properties and above all without facing increases of density,namely of the weight for the same mechanical strength with respect tothe known panels of the same type.

SUMMARY OF THE INVENTION

Therefore, the invention aims at providing thermoformable panels of thetype described hereinbefore able to overcome the drawbacks as regardsthe manufacturing aspect and structural, weight and cost aspects of theknown panels.

Particularly in the automotive industry, the current evolution is goingtowards a direction according to which panels that form variousaccessory or coating parts have to meet at best some requirements suchas for example they have to be thin, light, rigid (also at temperaturesfrom 80 to 90° C.), as well as not much expensive, and they have to showalso good acoustic insulation and waterproofing properties and have tobe produced with materials having a low emission of volatile substancesor of substances potentially harmful for the health.

The invention achieves the aims above by providing a thermoformablepanel composed of:

at least one core plate having a honeycomb structure which are arrangedwith their axes substantially parallel to each other and which areoriented substantially perpendicularly to the faces of said core plate;

a coating layer comprising at least one thermoplastic material iscoupled to said core plate on at least one face of said core plate,

and wherein the coating layer is composed of a film or a sheet ofthermoplastic material which is coupled to said core plate by achemical/physical adhesion, at least some of the head edges of the cellsof the core layer, for at least a part of their extension, havingsurfaces in contact and coupling with said film or sheet of the coatinglayer which have a size greater than the thickness of the walls of thematerial forming the cells.

According to a first embodiment, the invention provides the contactsurfaces between the material delimiting the cells of the honeycomb coreand a respective coating layer to be composed of the head edges of theshell walls that peripherally delimit the cells of the core plate and ofthe enlargements of said head edges in a direction parallel to the faceof the core plate and/or to the surface of the coating layer, that is ina direction transverse to the axis of the cells.

Such enlargements can be composed of end tabs of said head edgesextending transversely to the axes of the cells and connecting with nointerruption to the head edges of said walls delimiting the cells.

According to an advantageous embodiment, the enlargements or the tabsare obtained during the step coupling the coating layers. This stepprovides the compression lamination of the film or sheet ofthermoplastic material on the corresponding face of the core plate witha compression force that is adjusted such to partially bend to the sidethe head edges of the cells.

The compression force obviously changes depending on the materialforming the walls delimiting the cells.

Generally the honeycomb core plate is made of paper or paperboard or ofother natural fibers.

In order to make it easier to obtain such enlargements, according to animprovement, the invention provides to make the cells with head edgesindented toothed or segmented in a casual manner or according to apredetermined pattern or as an alternative or in combination to havecells whose head edges do not extend on the same plane, before couplingthe coating layers.

This allows the end portions of the cell walls to be bent in an easiermanner for generating the enlarged areas in contact with the coatinglayer by applying a lower compression force and therefore avoiding therisk of applying compression forces approaching the forces collapsingthe honeycomb core plate.

A second embodiment for making said enlargements of contact between thehoneycomb core plate and the coating layer or layers provides thecontact and coupling surfaces between the core plate and the coatinglayer for at least some of the cells and/or of a part of thecircumferential extension thereof to be composed of end portions of theshell wall delimiting the perimeter of the cells and of the head edgesof said wall.

In this case, the material of the coating layers having a predeterminedthickness is penetrated by the end head portions of the walls delimitingthe cells, and the contact between the material of the coating layersand the walls of the cells occurs also in the direction of the extensionof said walls parallel to the axis of the cells.

In this embodiment, the contact surfaces are obtained by a partialpenetration of the shell walls of the cells into the thickness of thecoating layer.

By suitably selecting thicknesses and thermoplastic materials of thecoating layers it is possible to obtain a combination of the twoembodiments of the enlarged contact areas between the honeycomb core andthe coating layers.

In both the embodiments, the chemical physical adhesion is such toguarantee that in case of bending no staggering is generated in thedirection parallel to the faces of the core plate, between the latterand the coating layers and therefore the panel obtained in this mannerhas a considerable stiffness.

According to a further improvement, the invention as an alternative orin combination with the characteristics shown above provides to usepreferred coating layers that help in enhancing the technical advantagesto which the invention is directed.

A first embodiment provides the coating layer to be composed of a nonwoven of a combination of different thermoplastic fibers, of which afirst type of thermoplastic fiber having a softening temperature(viscoelastic transition) lower than that of at least a secondthermoplastic fiber.

According to a further characteristic, the coating layer is composed ofa layer of continuous fibers of a thermoplastic polymer having a veryhigher softening temperature and of a film of a thermoplastic polymerhaving the softening temperature lower than said first thermoplasticpolymer.

In a preferred embodiment, the lower softening temperature ranges fromabout 90° C. to 120° C., while the higher softening temperature rangesfrom about 180° C. to 300° C., particularly from about 210° to 250° C.,preferably about 230/240° C.

According to a further improvement, on the external face of the coatinglayer, before coupling it to the core plate, contemporaneously with saidcoupling or after said coupling, a finishing layer is coupled made of athermoplastic material filled with vegetable and/or mineral fillers,particularly a coating layer of a mixture of polypropylene filled withwood flour.

In this first embodiment, the coating layer composed of the non woven ofplastic material fibers having a softening temperature higher than theplastic material of the film coupled to said non woven, formsinterstices among which the thermoplastic material with the lowersoftening temperature passes once the coating layer is brought in theviscoelastic condition by heating it, such that the plastic material ofthe film passes through the layer of non woven material and each fibersegment is embedded in the plastic material with the lower softeningtemperature, forming a kind of grid embedded in the thermoplasticmaterial with the lower softening temperature of the film and thereforea kind of reinforcement of the coating layer once the material iscooled.

According to an advantageous embodiment, it is preferred to provide aratio of the amount of thermoplastic material with the higher softeningtemperature to the amount of thermoplastic material with the lowersoftening temperature in the order of 0.6:1 up to 1:1.

In the panel made in this manner, the fiber contained in the coatinglayer of non woven material is used as a reinforcement fiber, since itsstiffness is considerably increased by the action stopping the relativemovement between the fibers in case of a stress exerted by the plasticmaterial.

In a further improvement the layer of non woven material is composed ofa web of continuous filaments extruded through a spinneret block, socalled spun bond non woven.

In one embodiment the thermoplastic material having the softeningtemperature higher than the thermoplastic material of the film iscomposed of polyester, particularly polyethylene terephthalate.

The film of thermoplastic material having the lower softeningtemperature in this case can be composed of polyolefin material or ofother polymers.

A further characteristic is the fact that the layer of thermoplasticmaterial forming the finishing layer has a thickness ranging from 0.5 to3 mm, preferably in the order of about 1 mm.

In a further embodiment the coating layer of non woven material has aweight lower than 150 gr/m², preferably ranging from 90 to 110 gr/m²,and a thickness lower than 100 particularly lower than or equal to 90μm.

The film associated to said non woven has a weight lower than 90 gr/m²,preferably lower than 70 gr/m², particularly lower or equal to 54 gr/m²and a thickness lower than 100 μm, particularly lower than 80 μmpreferably lower than or equal to 60 μm.

A second embodiment of the coating layer provides said coating layer tobe composed of a layer of thermoplastic material, particularlypolyolefins, especially of polypropylene filled with flours of vegetableand/or mineral fibers and having a softening temperature preferablyhigher than 90° C. to which a finishing layer composed of a film orsheet of thermoplastic fibers having a softening temperature rangingfrom 180° C. to 300° C., particularly from 210° C. to 240° C.,preferably of about 230/240° C. is coupled preferably before thecoupling on at least one of the two faces of the core plate, saidcoating layer being intended to be coupled with the core plate by theface opposite to that provided with the film or sheet of thermoplasticmaterial.

A further characteristic is the fact that the plate of thermoplasticmaterial has a thickness ranging from 0.5 to 3 mm, preferably in theorder of about 1 mm.

In one embodiment the coating layer is composed of a thermoplasticmaterial and of a fiber layer, the fiber layer being composed of such amaterial not to have changes in the state at the softening temperatureof the thermoplastic material.

According to an improvement, the film or sheet applied to the plate ofthermoplastic material is made of a non woven of a combination ofdifferent thermoplastic fibers, of which a first type of thermoplasticfiber having a softening temperature (viscoelastic transition) lowerthan that of at least a second thermoplastic fiber.

In one variant embodiment the fiber layer is composed of natural fibers.Natural fibers for example can be cotton, yucca, sisal, hemp, coco orthe like.

One embodiment provides said film to be composed of a layer ofcontinuous fibers of a thermoplastic polymer having a higher softeningtemperature and of a film of a thermoplastic polymer having thesoftening temperature lower than said first thermoplastic polymer.

According to this embodiment, the fibers are composed of the polymerhaving the higher softening temperature and are in the form of one layerof continuous fibers and/or of non woven, while the polymer having thelower softening temperature is in the form of a film. Moreover thedifference between the softening temperatures (temperature for thetransition to the viscoelastic condition) of the two polymers is suchthat, by heating said polymer combination, the polymer with the lowersoftening temperature gets “melted” while the polymer with the highersoftening temperature maintains its state and the continuous fibersmaintain their shape and/or structure. This results in the polymer withthe lower softening temperature occupying, by “pouring”, the intersticesamong the fibers composed of the polymer having the higher softeningtemperature that have maintained the shape and structure and that thusare embedded in the softened polymer having the lower softeningtemperature. In the cooling condition therefore the reinforcement layeris composed of continuous fibers composed of the thermoplastic materialwith the higher softening temperature embedded and locked in the polymerarray having the lower softening temperature.

According to a further characteristic the lower softening temperatureranges from about 90° C. to 120° C., while the higher softeningtemperature ranges from about 180° C. to 300° C., particularly fromabout 210° C. to 250° C., preferably it is of about 230° C.

As regards the film or sheet applied to the thermoplastic material layerof such second embodiment of the coating layer, said film or sheet canbe made according to what described above for the coating layeraccording to the first embodiment.

Still another optimization of the ratio of stiffness or mechanicalstrength to weight of the composite panel is obtained when in thereinforcement layer the ratio of the polymer with the higher softeningtemperature to the polymer with the lower softening temperature is from0.6:1 to 1:1.

The use of materials with a different softening temperature, of which atleast one material composed of natural or thermoplastic fibers, whenreaching the lower softening temperature allows an assembly to becreated wherein the fibers that have not been subjected to changes canslide with respect to each other allowing the panel to get deformed.When the temperature is again lowered under the softening value, thethermoplastic array solidifies again by locking the fibers in place.

Therefore the lamination temperature is selected within the softeningrange of the thermoplastic material with the lower softeningtemperature. Thus there is a better penetration between core, fibers andthe coating layer of further thermoplastic resin, if any.

The present invention further relates to a thermoformable panelcomprising a honeycomb core plate composed of a plurality of adjacentcells whose axes are oriented perpendicularly or substantiallyperpendicularly to the faces of said plate and to each face of said coreplate a coating layer is coupled which is composed of a film or sheet ofthermoplastic material having a softening temperature ranging from about180° C. to 300° C., particularly from about 210° C. to 250° C.,preferably of about 230° C.

In one embodiment said coating layer is composed of a layer ofcontinuous fibers of a thermoplastic polymer having the higher softeningtemperature and of a film of thermoplastic polymer having the softeningtemperature lower than said first thermoplastic polymer.

Said coating layer can have one or more of the characteristics describedabove for the coating layer according to the first embodiment.

In combination the thermoformable panel can have in combination also thecharacteristics of the enlarged surfaces of contact between the coreplate and the coating layer or layers.

On the contrary an alternative embodiment of the thermoformable panelprovides it to comprise a core plate composed of a plurality of adjacentcells whose axes are oriented perpendicularly or substantiallyperpendicularly to the faces of the said plate and to each face of saidcore plate a coating layer is coupled which is composed of a layer ofthermoplastic material particularly polyolefins, especiallypolypropylene filled with flours of vegetable and/or mineral fibres andhaving a softening temperature preferably higher than 90° C., preferablybefore the coupling on at least one of the two faces of the core plate,a layer composed of a film or a sheet of thermoplastic fibers having asoftening temperature ranging from 180° C. to 300° C., particularly from210° C. to 240° C., preferably of about 230° C., said coating layerbeing intended to be coupled to the core plate by the face opposite tothat provided with the film or sheet of thermoplastic material.

In an alternative embodiment the sheet is composed of a layer comprisinga first thermoplastic polymer with high polarity and a secondthermoplastic polymer with high resilience.

This guarantees an optimal adhesion due to the high polarity of thefirst polymer and a contemporaneous good strain and wear strength due tothe high resilience of the second polymer.

In a preferred example the first polymer is polyvinyl alcohol and thesecond polymer is polyamide.

In a further improvement the layer has a content of mineral or vegetablefiller. As the filler it is possible preferably to use wood flour, ortalc or other types of fillers currently known in the art. The fillerallows the panel strength to be improved.

The invention further relates to an intermediate thermoformable panelcomposed of a coating layer on one of the two faces that coplanar withsaid face has perimetral tabs projecting beyond the peripheral edges ofthe core plate, while on the opposite face of the core plate, thecoating layer applied thereon overlaps by coupling thereto also theperipheral edges of said core plate and to the perimetral tabsprojecting beyond the peripheral edges.

Thus a thermoformable panel is obtained that on all the sides, that isthe two faces and the peripheral edges is coated by the material of thecoating layer the shape and the dimensions of the core plate beingrecognizable on one face such to facilitate the correct positioning forexample into the mold of a forming press.

The present invention further relates to a method for making athermoformable panel according to what described above which methodcomprises the following steps:

step a) coupling on one or two faces of a honeycomb core plate a coatingfilm by chemical physical adhesion thereto of said film, which film ismade according to one or more of the variants described above;

step b) subsequently coupling on one of the two faces of the core plateto the corresponding coating film a finishing layer such as describedabove.

According to a further characteristic of the method, in step a, thecoupling occurs in a laminator at a heating temperature ranging from180° C. to 300° C., particularly from 210° C. to 240° C., preferably ofabout 230° C.

Moreover step b) is performed at a softening temperature higher than 90°C., preferably at 180° C. particularly ranging from about 210° to 240°C., preferably at about 230° C.

According to one embodiment step b) provides to contemporaneouslythermoform the panel in a mold according to a three-dimensional patternof the panel.

A variant of said method provides the following steps:

a1) cutting to size the honeycomb core plate according to predetermineddimensions;

a2) cutting to size a first and a second coating layers with an areagreater than that of the honeycomb core plate

a3) centrally arranging the honeycomb core plate on a first finishinglayer such that a peripheral band of said first layer projects beyondthe peripheral edge of the honeycomb core layer by a predeterminedamount and preferably along the entire peripheral edge of the honeycombfinishing plate;

a4) arranging on the top face of the honeycomb core plate the secondcoating layer, by placing it in a position substantially congruent withthe first coating layer;

a5) bending the second coating layer about the core plate, along theperipheral edges of said honeycomb core plate and against the firstcoating layer, by means of a bending frame of said second top coatinglayer;

a6) coupling the coating layers to the faces of the core plate and tothe peripheral edges of said core plate, as well as coupling theprojecting parts of said first and second coating layers with each otherby hot lamination, during the lamination keeping said assembly of coreplate and coating layers in said bending frame.

Still a variant embodiment of the method provides the steps:

step c) coupling on one of the two faces of a plate of thermoplasticmaterial, particularly polyolefins, especially polypropylene filled withflours of vegetable and/or mineral fibers and having a softeningtemperature preferably higher than 90° C. a layer in the form of athermoplastic fiber film having a softening temperature ranging from180° C. to 300° C., particularly from 210° C. to 240° C., preferably ofabout 230° C.,

step d) coupling said coating layer on one or both the faces of the coreplate by the face opposite to that provided with the film or the sheetof thermoplastic material by hot lamination and/or in athree-dimensional modelling process by hot molding or rolling process,hot calendering.

BRIEF DESCRIPTION OF DRAWINGS

These and other characteristics and advantages of the present inventionwill be more clear from the following description of some non limitativeembodiments shown in the annexed drawings wherein:

FIG. 1 schematically is the structure of a thermoformable panel with ahoneycomb core plate according to a first embodiment of the presentinvention.

FIG. 2 is a variant embodiment of the steps for coupling the coatinglayers to the faces of the honeycomb core plate.

FIG. 3 schematically is an enlarged section of the thermoformable panelaccording to this first embodiment.

FIG. 4 schematically is an enlarged section of the panel according asecond embodiment of the present invention.

FIG. 5 is, like the previous figures, a combination of the variantembodiments according to FIGS. 3 and 4.

FIGS. 6 to 8 show respectively the steps of applying the coating layersto a honeycomb core plate for making a thermoformable panel according toa fourth embodiment of the present invention.

FIG. 9 schematically shows the step of three-dimensional forming of thethermoformable panel according to the embodiment of the previous FIGS. 3to 5 by a mould.

DESCRIPTION OF EMBODIMENTS

The description below shows several variant embodiments of the panelaccording to the present invention. These variants are not to beconsidered as a limitation, but merely as an illustration of theinventive concept that consists in providing a thermoformable panel witha honeycomb core plate on at least one of its faces a coating layer ofplastic material is applied, preferably by lamination or the like suchto avoid the different mechanical properties of the honeycomb core plateand of the coating layer or layers—depending on the core plate beingriveted on one or two faces—causing said layers to separate from eachother at least partially at different areas upon bending, due to arelative displacement in a direction parallel to the contact surfaces,thus guaranteeing an optimal stiffness in connection with a limitedweight and with the use of less expensive plastic materials.

Although the examples show the presence of coating layers on both thefaces of the honeycomb core plate, it is also possible that only one ofthe faces is coupled to a coating layer or that different coating layersare coupled to the two faces depending on the different embodimentsthereof provided in the present description.

FIG. 1 shows a first embodiment wherein a honeycomb core plate 1 iscoupled on both the faces with a coating layer 2.

The honeycomb core plate is preferably made of paperboard or similarmaterials and it is obtained according to known techniques.

Each one of the coating layers 2 is composed of at least two layers,preferably three layers of which at least one layer 202 composed of anon woven of fibers of a first thermoplastic polymer and at least onesecond layer is composed of a film 201 of a second thermoplastic polymerdifferent than the thermoplastic polymer the fibers of the non woven aremade of and having a softening temperature (viscoelastic transition)lower than that of the thermoplastic polymer the fibers of the non wovenare made of.

Particularly the second thermoplastic polymer has the lower softeningtemperature ranging from about 90° C. to 120° C., while the firstthermoplastic polymer the fibres of the non woven are made of has ahigher softening temperature ranging from about 180° to 300°,particularly from about 210° to 250°, preferably of about 230°.

In FIG. 1 there are provided two films 202 composed of the secondthermoplastic polymer the non woven layer with fibres of the firstthermoplastic polymer is provided therebetween.

The PET non woven 201 is coated with 2 films that have a double effectand that is to stop the sliding of the fibers when are subjected to aforce, an effect that is obtained also by using a mix of two fibers witha different molecular weight and therefore with different softeningtemperatures, such as described above and also to guarantee the adhesionon the two interfaces (the one with the honeycomb 1 and the above onewith the wood-stock plate 4). The PET-based films 202 further guaranteethe finished panel, during tests at 80/90° C., to withstand bending inthe automotive industry.

According to one embodiment and such as pointed out in FIG. 2, thecoupling of the coating layer or layers 2 to the honeycomb core plate 1occurs for example by hot lamination.

Preferably the coupling occurs in a laminator at a heating temperatureranging from 180° C. to 300° C., particularly from 210° C. to 240° C.,preferably at about 230° C.

In these conditions, the polymer with the lower viscoelastic transitiontemperature penetrates into the interstices of the fibers of the nonwoven. The latter remain substantially entire since they are composed ofa polymer having a higher softening temperature. Thus the fibers aresurrounded by the mass of the polymer with a lower softening temperatureand are embedded therein forming a reinforcing grid that remains firmlyanchored into the material of the polymer having the lower softeningtemperature upon cooling. Contemporaneously, the pressure exerted in thelamination against the honeycomb core plate 2 is such to generate twopossible effects that can be provided both individually andalternatively and in combination with each other.

FIGS. 3 and 5 show such situation.

FIG. 3 schematically shows a section of a panel according to the presentinvention, wherein in addition to the coating layers there are providedthe external finishing layers 4 one on each of the coating layers 2.

Moreover in the case of FIG. 3, the pressure applied for coupling thecoating layer to the core plate 1 has partially deformed the head edgesof the shell walls 201 of the cells, forming transverse tabs 101 thatwiden the contact surface between the core plate 2 and the coatinglayers 1.

Such effect can be promoted by making the head ends of the cells withhead edges that are indented and/or not all coplanar with each other.

According to a variant embodiment from FIG. 2, in order to avoid thecore plate 2 to be excessively pressed it is possible to provide one ormore material inserts, such as wood or the like whose thicknesscorresponds to the finished thickness of the core plate and thattherefore form incompressible stops such to protect the honeycomb coreplate against such a pressure that can cause the structure to collapse.Such inserts may be used also for fastening components made of plasticor metal on the external surface of the finished shelf by means ofscrews.

In a preferred embodiment, the honeycomb core plate is made ofpaperboard or the like.

It may have a thickness from about one to several centimeters.

As regards the coating layer one embodiment provides the non woven layerto be composed of fibers of polyester, particularly polyethyleneterephthalate.

The films 201 of thermoplastic material with a lower softeningtemperature for example are composed of polyolefin material or otherpolymers.

The non woven material layer has a weight lower than 150 gr/m²,preferably lower than 100 gr/m², particularly lower than or equal to 90gr/m², and a thickness lower than 100 particularly lower than or equalto 90 μm.

The film associated to said non woven has a weight lower than 90 gr/m²,preferably lower than 70 gr/m², particularly lower than or equal to 54gr/m², and a thickness lower than 100 particularly lower than 80preferably lower than or equal to 60 μm.

The honeycomb core plate is made of paperboard or similar materials,while the finishing layer can be made of different materials, and in apreferred variant it is composed of thermoplastic material, particularlypolyolefins, especially polypropylene filled with flours of vegetableand/or mineral fibers.

In one embodiment, the finishing layer 4 is applied to the panel, on oneof the external faces of one of the coating layers 2 after coupling thecoating layers to the honeycomb core plate 1.

The variant of FIG. 4 can be provided at least partially also by using acoating layer such as that described with reference to FIGS. 1 to 3,however it is possible to provide the coating layer to be composed of aplate of thermoplastic material 5, particularly a plate of polyolefins,especially polypropylene filled with flours of vegetable and/or mineralfibers and having a softening temperature preferably higher than 90° C.

To such plate a finishing layer 6 is in turn coupled which is composedof a film or a sheet of thermoplastic fibers having a softeningtemperature ranging from 180° C. to 300° C., particularly from 210° C.to 240° C., preferably of about 230° C.

Particularly the finishing film 6 is composed of a combination of twothermoplastic polymers each one having a different viscoelastictransition temperature and that is a higher one and a lower one.

Still according to a further characteristic the finishing layer 6 ismade according to one or more of the variants described for the coatinglayer 2 of the previous embodiment according to FIGS. 1 to 3.

The thermoplastic plate composed of polyolefins, preferablypolypropylene, filled with flours of vegetable and/or mineral fibers isinitially coupled only with the finishing film. The combination ofthermoplastic plate 5 and finishing layer 6 then is coupled together tothe honeycomb core plate 1 forming its coating layer, the face of thethermoplastic material plate 5 and the face of the core plate 1 beingput in contact.

In this case, since the thermoplastic material plate 5 has a lowviscoelastic transition temperature, the end portions of the walls 102delimiting the cells penetrate into the thickness of the thermoplasticmaterial plate 5 partially embedding therein and for a given amountdefined by the exerted compression.

This situation is shown in FIG. 4 where said end portions on the headsides of the cells 102 that are denoted by 301 penetrate into thethickness of the material of the thermoplastic material plate 5.

When the finishing layer is made as described with reference to theexample in FIGS. 1 to 3, due to the higher viscoelastic transitiontemperature, said layer remains substantially not penetrable by the endportions 301 of the walls 102 delimiting the cells.

By applying a suitable coupling compression, it is possible to obtain acombination of effects of enlarging the contact surfaces between coreplate 1 and coating layer composed of the combination of the layers 5and 6. In this case as it results from FIG. 5 in addition to the layer 5penetrated by the end portions 301 of the walls of the cells 102, theseend portions also bent at least for a part forming transverse tabs 101.

It has to be noted that in FIGS. 4 and 5 the walls 102 of the cellspenetrate through the thickness of the thermoplastic material plate upto the finishing layer 6. However both in the variant of FIG. 4 and inthat of FIG. 5, it is possible for some of the cells to have the headedge and/or the associated transverse tab to end at a given distancefrom the finishing layer 6.

This depends on the initial coplanarity of the head edges of the wallsdelimiting the cells in the core plate 1 or also on the provision of apreventive treatment of the core plate 1 making the head edges of thewalls 102 delimiting the cells as indented, toothed or not coplanaranyway.

With reference to FIGS. 6 to 8, they show the steps for making athermoformable panel with a honeycomb core according to a furthervariant of the present invention.

In this case the panel has a honeycomb core plate 1 closed at all thesides, that is also along the perimetral edge by a coating layer 2 whichis made according to one of the different variants described.

In this case the thermoformable panel obtained is a kind of blank panelthat is an intermediate product that can be stored and used incombination with other material layers, such as for example one or morefinishing layers 4, for making three-dimensionally shaped parts, forexample by molding.

For producing such panel, it is provided to cut to size the honeycombcore plate 1 and sheets of material intended to form the coating layersaccording to one or more of the preceding embodiments, the latter havingdimensions greater than those of the core plate 1.

A first sheet composed of the material layers according to one of thepreceding examples is arranged on a plane and the core plate 1 isplaced, centered thereon. On the upper face of the core plate 1therefore the further sheet or assembly of sheets intended to form thecoating layer 2 of the upper face of the core plate 1 is placed.

A frame 7 vertically movable from an idle position to a position whereit surrounds all the perimetral edge of the core plate bends, during itstranslation, the sheet or the assembly of sheets intended to form theupper coating layer 2, this sheet or these sheets also against theperimetral edge and it compresses the remaining perimetral edge of saidsheet or said assembly of sheets against the sheet or assembly of sheetsintended to form the lower coating layer 2.

This assembly in the condition described and shown in FIG. 7 is placedon the laminator for applying the layers 2 to the honeycomb core plate 1by lamination. During the lamination also the peripheral parts 302 ofthe two coating layers 2 that surround the perimetral edge of the coreplate 1 are coupled with each other by chemical/physical adhesionprojecting beyond said perimetral edge and thus forming a thermoformablepanel with the honeycomb core completely coated and with a perimetralframe extending coplanar with one of the two faces.

This embodiment has the advantage that the shape of the core plate 1remains easily recognizable and therefore the proper positioning of thethermoformable panel in a mold is considerably facilitated for theadditional treatment, such as shown in FIG. 9.

This figure shows a mold 8 and a countermold 9 having forming surfaceswith a predetermined three-dimensional profile denoted by 108 and 109.As it is possible to see since the shape of the core plate 1 isrecognizable it is possible to properly house the thermoformable panelrelative to the molds.

In FIG. 9, the forming step provides contemporaneously the step ofapplying further external finishing layers 4 according to one or more ofthe embodiment described above.

In this case the fact of extending the two coating layers 2 with respectto the surface of the honeycomb core plate 1, not only helps the sideedges thereof to be covered with the coating layer that improves theadhesion of the finishing layer 4 also along the edges and thereforethat guarantees a higher mechanical strength, but it helps also tostiffen the two external finishing plates 4 that are sealed with eachother along the perimeter of the panel during the thermocompressionstep. In this case the coating layers 2 and particularly the non wovenlayers 201 and the films 202 remain compressed along the edges betweenthe two plates, forming a stronger perimetral edge of the panel. Suchperimetral edge can be provided with different sectional shapes, forexample with a U-shaped cross-section instead of a flat one as in thedrawing.

The invention claimed is:
 1. A thermoformable panel comprising: a coreplate having a honeycomb structure, which comprises a plurality ofadjacent cells arranged with their axes substantially parallel to eachother and substantially perpendicular to opposing faces of the coreplate; a thermoplastic polymer film bonded to at least one of the facesof the core plate; and a second layer bonded to a face of thethermoplastic polymer film, which is opposed to the core plate; whereinthe second layer comprises a nonwoven layer of continuous thermoplasticpolymer fibers embedded in a thermoplastic material; wherein at leastsome of the core plate cells have head edges which at least partiallypenetrate into the thermoplastic polymer film; wherein at least some ofthe head edges have enlargements in a direction transverse to the axisof the cells.
 2. The panel of claim 1, wherein the thermoplastic polymerfilm comprises a thermoplastic polyolefin and vegetable and/or mineralfibers.
 3. The panel of claim 1, wherein the core plate comprises aplurality of cells peripherally delimited by a shell wall made ofnatural fibers.
 4. The panel of claim 1, wherein thermoplastic materialhas a lower softening temperature and the continuous thermoplasticpolymer fibers have a softening temperature which is higher than thelower softening temperature.
 5. The panel of claim 4, wherein the lowersoftening temperature is about 90 to 120° C. and the continuousthermoplastic polymer fibers have a softening temperature of about 180to 300° C.
 6. The panel of claim 1, wherein the ratio of the continuousthermoplastic polymer fibers to the thermoplastic material is 0.6:1 to1:1.
 7. The panel of claim 1, wherein the thermoplastic polymer filmcomprises polypropylene filled with wood flour.
 8. The panel of claim 1,wherein the non-woven layer has a weight of less than 150 g/m² and athickness of less than 100 μm.
 9. The panel of claim 1, wherein thethermoplastic polymer film has a thickness of about 0.5 to 3 mm.
 10. Thepanel of claim 1, wherein the continuous thermoplastic polymer fiberscomprise polyester fibers and the thermoplastic material comprisespolyolefin.
 11. The panel of claim 1, wherein the continuousthermoplastic polymer fibers comprise polyethylene terephthalate fibersand the thermoplastic material comprises polypropylene.
 12. The panel ofclaim 1, wherein the thermoplastic polymer film is bonded to a firstface of the core plate; and a second thermoplastic polymer film isbonded to an opposing face of the core plate; and a third layer isbonded to a face of the second thermoplastic polymer film, which isopposed to the core plate; wherein the third layer comprises a nonwovenlayer of continuous thermoplastic polymer fibers embedded in athermoplastic material; wherein at least some of the core plate cellshave head edges which at least partially penetrate into the secondthermoplastic polymer film.
 13. The panel of claim 1, wherein the coreplate comprises a plurality of cells peripherally delimited by a shellwall made of natural fibers; the thermoplastic polymer film has athickness of about 0.5 to 3 mm and comprises polypropylene filled withwood flour and/or talc; the non-woven layer has a weight of less than150 g/m² and a thickness of less than 100 μm; and the continuousthermoplastic polymer fibers comprise polyethylene terephthalate fibersand the thermoplastic material comprises polypropylene.
 14. A method formaking the thermoformable panel of claim 1, comprising the followingsteps: coupling the second layer on a first face of the thermoplasticpolymer film; and subsequently coupling a second face of thethermoplastic polymer film on a face of the core plate such that atleast some head edges of the core plate cells at least partiallypenetrate into the thermoplastic polymer film.
 15. A thermoformablepanel comprising: a core plate having a honeycomb structure, whichcomprises a plurality of adjacent cells arranged with their axessubstantially parallel to each other and substantially perpendicular toopposing faces of the core plate; wherein at least some of the coreplate cells have head edges with enlargements in a direction transverseto the axis of the cells; a coating layer bonded to enlarged head edgeson one of the core plate faces; wherein the coating layer comprises anonwoven layer of continuous thermoplastic polymer fibers embedded in athermoplastic material; and a thermoplastic polymer film bonded to aface of the coating layer, which is opposed to the coating layer facebonded to the core plate; wherein the thermoplastic polymer filmcomprises thermoplastic polyolefin and vegetable and/or mineral fibers.16. The panel of claim 15, wherein the thermoplastic polymer film has athickness of about 0.5 to 3 mm and comprises polypropylene filled withwood flour.
 17. The panel of claim 15, wherein the continuousthermoplastic polymer fibers comprise polyester fibers having asoftening temperature of about 210 to 250° C. and the thermoplasticmaterial comprises polyolefin having a softening temperature of about 90to 120° C.
 18. The panel of claim 15, wherein the continuousthermoplastic polymer fibers comprise spun bond, non-woven polyethyleneterephthalate fibers; the thermoplastic material comprisespolypropylene; and the thermoplastic polymer film comprisespolypropylene filled with wood flour and/or talc.
 19. A thermoformablepanel comprising: a core plate having a honeycomb structure, whichcomprises a plurality of adjacent cells arranged with their axessubstantially parallel to each other and substantially perpendicular toopposing faces of the core plate; wherein at least some of the coreplate cells have head edges with enlargements in a direction transverseto the axis of the cells; a coating layer bonded to the enlarged headedges on at least one of the core plate faces; wherein the coating layercomprises a nonwoven layer of continuous thermoplastic polymer fibershaving a softening temperature of about 180 to 300° C. embedded in athermoplastic material, which has a softening temperature of about 90 to120° C.
 20. The panel of claim 19, wherein at least some of the headedges with enlargements at least partially penetrate into the coatinglayer.
 21. The panel of claim 19, wherein the thermoplastic materialcomprises thermoplastic polyolefin; and the nonwoven layer comprisesnon-woven polyester fibers.
 22. The panel of claim 19, wherein thethermoplastic material comprises polypropylene filled with wood flourand/or talc; and the nonwoven layer comprises spun bond, non-wovenpolyethylene terephthalate fibers.
 23. The panel of claim 19, furthercomprising a finishing layer bonded to an external face of the coatinglayer on one face of the core plate; wherein the finishing layercomprises polypropylene filled with wood flour and/or talc.
 24. Thepanel of claim 19, wherein the coating comprises a first thermoplasticpolymer that is polyvinyl alcohol and a second thermoplastic polymerthat is polyamide.
 25. The panel of claim 19, wherein the core platecomprises a plurality of cells peripherally delimited by a shell wallmade of natural fibers; the non-woven layer has a weight of less than150 g/m² and a thickness of less than 100 μm; and the continuousthermoplastic polymer fibers comprise polyethylene terephthalate fibersand the thermoplastic material comprises polypropylene.